This invention relates to a simple and reliable mechanical tool for inserting medical electrodes into nerve tissue such as the cerebral cortex, brain stem and the spinal cord. The tool can be hand held, or mounted in a stereotactic positioning device. An alternative embodiment of the tool uses a curved tip for holding the electrode for insertion in the cochlear nucleus of the brain as part of a procedure to assist a profoundly deaf patient.
The tool is especially useful with small medical electrodes having a button-like cylindrical base, typically made of epoxy, of about 2.5-mm diameter and about 0.5-mm thickness. Typically, multiple (e.g., seven) relatively sharp time-like electrodes (the length depending on the application, but typically in the range of 1 to 6 mm) extend from the base, and connecting leads enable individual or parallel energization of the electrodes depending on the nerve-stimulation protocol being used.
The challenge met by the invention is to move the positioned electrode with an initially high acceleration to enable the electrode times to penetrate at high velocity the tough and puncture-resistant pia-arachnoid member overlapping the cortex and spinal cord. It is then desirable to stabilize and cease accelerating the penetration rate to prevent injury to the underlying neuron al population, and to the delicate arterial and venous blood vessels.
An important advantage of the invention is that the electrodes and associated base are recessed within a tip of the insertion tool prior to actuation. This feature enables the tool tip to be positioned against the tissue to be penetrated, thus enabling handheld operation as opposed to the sometimes cumbersome mounting of the tool in a stereotactic positioning device.
Several alternative velocity-control mechanisms are disclosed which approximate viscous damping of movement of the electrode driving mechanism to enable high initial acceleration until penetration is achieved, with controlled and relatively stabilized velocity thereafter.